1. Field of the Invention
The present invention concerns a translucent sheet laminated article comprising a textile net middle layer between two cover layers each composed of translucent film.
2. The Prior Art
Translucent sheets are used for tents, marquees, construction sheeting or roofing paper. Products that are very mechanically stable consist of several layers. The layered structure comprises a textile, net-like middle layer and two cover layers that enclose the textile middle layer. The textile middle layer provides mechanical stability. The net-like structure also allows light to pass through. The two cover layers made of transparent films fix the textile net-like middle layer and seal against water and wind.
To absorb force in the primary direction of stress, the fibers of the textile, net-like middle layer must extend in the main direction of stress. During production, particularly high force arises in the direction of production. However, force can also arise when the finished sheet is used that may be concentrated in one particular direction. Such force can result e.g. from wind or precipitation.
Meeting the mechanical requirements has limited the design of the network. The design has therefore been limited to rectangular and square meshes. This design is insufficient for decorative products because the mesh is visible due to the translucence of the sheet.
It is an object of the present invention to provide an improved translucent sheet that allows greater freedom in designing the mesh while retaining mechanical stability.
The above object is achieved by providing a translucent sheet laminated article comprising a top cover layer made of a translucent film; a bottom cover layer made of a translucent film; a textile net middle layer that is between said two cover layers having areas of a mesh of the textile net middle layer which are at an angle to a main direction of stress, and said middle layer having stabilizing threads aligned with the main direction of stress, and said stabilizing threads are bonded to areas or knots of the textile net middle layer that run in the same direction as said threads.
In the laminated article according to the invention, the mesh can have any design. When areas of the mesh of the textile net middle layer are at an angle to the main direction of stress and cannot therefore absorb force in the main direction of the stress, the stabilization threads in the main direction of force absorb the force completely. This also means that the mesh shape intended by the designer is retained during production. Hence the mesh is not distorted by forces arising in production.
The sandwich structure of the textile net middle layer and the cover layers yields a basic mechanical strength after production. The stabilizing threads increase strength in the direction in which they run. When there is a main direction of stress, the translucent sheet is aligned so that the stabilizing threads run in the main direction of stress.
In one embodiment of the invention, the cross-section of the fibers forming the mesh is greater than the cross-section of the stabilizing fibers. The bond of the fibers forming the mesh to the cover layers therefore becomes tighter. At the same time, the stabilizing fibers become less visually prominent than the fibers forming the mesh.
The mesh can be polygonal. This produces a type of honeycomb pattern in which parts of the mesh form parts of adjacent mesh. This produces a favorable ratio between the open and hence translucent areas of the mesh and the areas occupied by the fibers of the mesh. A particularly high basic strength results from the bond between the textile net middle layer and the cover layers in all directions within the plane of the sheet.
The mesh width can be 2 mm to 10 mm. This dimension represents an optimum compromise between light permeability and mechanical strength.
The textile net middle layer preferably comprises a knit. This type of textile yields a particularly good bond between the individual fibers forming the mesh and the stabilizing fibers.
The fibers of the mesh can be a multitwisted monofilament yarn. This improves the bonding of the knots of the mesh to themselves and the bond between the fibers of the textile middle layer and the cover layers.
The material of the textile net middle layer can comprise synthetic raw materials, preferably polyester, polyamide, polyaramide, polyimide or mixtures thereof. These raw materials have a reduced tendency to stretch and yield under tension. This ensures that the sheet retains its form and shape under stretching.
The material of the textile net middle layer can be colored. This allows the textile structure to be visually distinguished from the stabilizing threads so that the stabilizing threads become practically invisible. In. addition, the overall sheet can be in the form of an ornamental structure.
The textile net middle layer can be 0.3-0.6 mm thick, and preferably 0.35 mm thick. This dimension represents the best compromise between mechanical strength and flexibility, i.e., its bending or folding property.
The two cover layers are preferably comprised by a thermoplastic material, and they are melted together through the meshes of the textile net middle layer to form the laminated article. This produces a very precise geometric structure of the sheet that ensures that the textile net middle layer assumes a precise position between the two cover layers. In addition, a tight bond between the cover layers is ensured.
The thermoplastic can be made with a calender or extruder. This embodiment produces a very homogenous cover layer with a uniform thickness.
The thermoplastic material is preferably comprised by soft PVC, thermoplastic olefins or polyurethane. This material is particularly yielding and adheres well to provide a tight bond to the textile material.
In another embodiment, it is possible for at least the top cover layer to contain antioxidants and UV absorbers and/or IR absorbers. This ensures long life while maintaining the useful properties even when the sheet is continuously exposed to the weather and to sunlight.
In a further embodiment, one of the cover layers can contain a color agent, such as dyes and/or pigments. It is also possible for the two cover layers to contain different dyes and/or pigments. In addition to decorative possibilities for the sheet, the light permeability, or the color of the transmitted light and the permeability to or absorption/reflection of IR or UV rays can be influenced.
The cover layers can be 0.3-0.45 mm thick and preferably 0.35 mm thick depending on the middle layer. This dimension for the thickness of the cover layers provides sufficient cover and encasing for the fibers of the middle layer.
In a further embodiment, at least one of the cover layers can have an embossed surface. This increases the construction possibilities of the sheet and influences the stability and bendability of the sheet.
In another embodiment, the top cover layer can have an additional translucent varnish coating or layer thereon. This varnish layer can protect the cover layer. In particular, it protects against microorganisms that can collect on the surface under the influence of weather in the form of moss or algae.